The vm2 Node.js sandbox prior to version 3.11.4 contains a protection mechanism failure (CWE-693) in the BaseHandler.set trap implementation within bridge.js. The set trap does not respect the receiver parameter as required by the Proxy specification. When the receiver is different from the proxy (such as when a child object inherits from the proxy), property assignments incorrectly write directly to the host target object instead of creating an own property on the receiver. This flaw allows attackers to write dangerous cross-realm Symbol keys (e.g., nodejs.util.promisify.custom) to host objects, circumventing potential future security guards on direct set operations. The vulnerability is rated high severity with a CVSS 3.1 score of 8.6 and was fixed in vm2 version 3.11.4.

Exploitation of this vulnerability can lead to unauthorized modification of host objects by writing dangerous cross-realm Symbol keys. This undermines the sandbox's isolation guarantees and could allow attackers to bypass security checks that rely on property assignment controls. The vulnerability does not impact confidentiality or availability directly but poses a high integrity risk within the sandbox environment.

A fix for this vulnerability is available in vm2 version 3.11.4. Users should upgrade to version 3.11.4 or later to remediate this issue. No other mitigation steps are indicated by the vendor advisory or source data.